District 230 officials are not 100 percent sure what caused a strange smell that led to the evacuation of Stagg High School on Dec. 4 but they have some theories. Stagg Principal Eric Olsen sent out a phone message and letter to parents about what may have happened and research showed it could have been an outside force. “Based upon all available information, we cannot be certain as to the cause of the carbon monoxide exposure students and staff experienced…however, given the weather conditions on Dec. 4, it is possible that due to the warm, foggy air that was stagnant in the morning, carbon monoxide from local traffic around the building may have built up and been pulled into the school’s fresh air intake for the HVAC system on the affected side of the building,” Olson said. “Although the cause of the incident is not definitive, the district has decided to place carbon monoxide detectors in several fresh air intakes surrounding the building that would notify personnel if carbon monoxide levels were detected and would shut down outside air intake. While this process is being completed, school personnel will regularly check the carbon monoxide levels in the building to ensure student and staff safety.” First responders arrived on the scene that day shortly after the 1 p.m. emergency phone call was made, and the Palos Hills Police Department had blocked off Roberts Road, south of 111th Street, with the school being on the southwest corner of that intersection. Besides the North Palos Fire Department, several surrounding area first responders arrived on site including: Orland Park, Evergreen Park, Hometown and a HAZMAT team from Bedford Park. EMS first responders also arrived on site from surrounding areas, including: North Palos, Roberts Park, Bridgeview, Chicago Ridge and Palos Heights. Three Nicor trucks also responded to the call, according to Stagg school officials. The emergency vehicles began leaving the school grounds shortly after 2 p.m., according to school officials. Seven people were transported by ambulance from the school — six students and one staff member. These individuals were transported as a precaution. The school reopened to students the next day. Public safety agencies found no gas leaks inside Stagg, Olsen noted. “Carbon monoxide has never been detected inside of the school building by district, emergency, or outside environmental and mechanical engineering personnel,” Olsen said. “However, District 230 has always believed that the safety of everyone who utilizes our facilities is paramount, and we believe that the steps we are taking in consultation with experts in the field are a proactive measure to assure student and staff safety.’’